Immunisation with the glycolytic enzyme enolase confers effective protection against Candida albicans infection in mice

A novel quantitative double antigen sandwich ELISA for detecting total antibodies against Candida albicans enolase 1

PURPOSE

This study aimed to develop a double antigen sandwich ELISA (DAgS-ELISA) method for more efficient, accurate, and quantitative detection of total antibodies against Candida albicans enolase1 (CaEno1) for diagnosing invasive candidiasis (IC).

METHODS

DAgS-ELISA was developed using recombinant CaEno1 and a monoclonal antibody as the standard. Performance evaluation included limit of detection, accuracy, and repeatability. Dynamic changes in antibody levels against CaEno1 in serum from systemic candidiasis mice were analyzed using DAgS-ELISA. Patient serum samples from IC, Candida colonization, bacterial infections, and healthy controls were analyzed with DAgS-ELISA and indirect ELISA.

RESULTS

DAgS-ELISA outperformed indirect ELISA in terms of linear range and test background. In systemic candidiasis mice, a distinctive 'double-peak' pattern in dynamic antibody levels was observed. Additionally, there was a high level of consistency in the positive rates of CaEno1 antibodies detected by both DAgS-ELISA and indirect ELISA. While the positivity rates differed among patient groups, no significant variations in antibody levels were detected among the various positive patient groups.

CONCLUSIONS

DAgS-ELISA offers a reliable novel approach for IC diagnosis, enabling rapid, accurate, and quantitative detection of CaEno1 antibodies. Further validation and optimization are needed for its clinical application and effectiveness.

Molecular cloning, expression, and purification, along with in silico epitope analysis of recombinant enolase proteins (a potential vaccine candidate) from Candida albicans and Candida auris

Candida albicans is the predominant cause of systemic candidiasis, although other non albicans Candida species are progressively becoming more widespread nowadays. Candida auris has emerged as a deadly multidrug-resistant fungal pathogen, posing a significant threat to global public health. In the absence of effective antifungal therapies, the development of a vaccine against C. auris infections is imperative. Enolase, a key glycolytic enzyme, has emerged as a promising vaccine candidate due to its immunogenic properties and essential role in fungal virulence. Herein, full-length Enolase gene sequences from C. albicans and C. auris were cloned into suitable expression vector and transformed into Escherichia coli expression hosts. Recombinant Enolase proteins were successfully expressed and purified using affinity chromatography under native conditions, followed by SDS-PAGE characterization and Western blot analysis. CD spectroscopy verified the existence of expressed proteins in soluble native conformation. Preliminary in silico studies verified the immunogenicity of recombinant Enolase proteins isolated from both C. albicans and C. auris. Furthermore, bioinformatics analysis revealed conserved B-cell and T-cell epitopes across C. albicans and C. auris Enolase proteins, suggesting potential cross-reactivity and broad-spectrum vaccine efficacy. Our findings are anticipated to play a role in advancing therapeutic as well as diagnostic strategies against systemic candidiasis.

Identification of the Most Immunoreactive Antigens of Candida auris to IgGs from Systemic Infections in Mice

The delay in making a correct diagnosis of Candida auris causes concern in the healthcare system setting, and immunoproteomics studies are important to identify immunoreactive proteins for new diagnostic strategies. In this study, immunocompetent murine systemic infections caused by non-aggregative and aggregative phenotypes of C. auris and by Candida albicans and Candida haemulonii were carried out, and the obtained sera were used to study their immunoreactivity against C. auris proteins. The results showed higher virulence, in terms of infection signs, weight loss, and histopathological damage, of the non-aggregative isolate. Moreover, C. auris was less virulent than C. albicans but more than C. haemulonii. Regarding the immunoproteomics study, 13 spots recognized by sera from mice infected with both C. auris phenotypes and analyzed by mass spectrometry corresponded to enolase, phosphoglycerate kinase, glyceraldehyde-3-phosphate dehydrogenase, and phosphoglycerate mutase. These four proteins were also recognized by sera obtained from human patients with disseminated C. auris infection but not by sera obtained from mice infected with C. albicans or Aspergillus fumigatus. Spot identification data are available via ProteomeXchange with the identifier PXD049077. In conclusion, this study showed that the identified proteins could be potential candidates to be studied as new diagnostic or even therapeutic targets for C. auris.

Application of anti-fungal vaccines as a tool against emerging anti-fungal resistance

After viruses and bacteria, fungal infections remain a serious threat to the survival and well-being of society. The continuous emergence of resistance against commonly used anti-fungal drugs is a serious concern. The eukaryotic nature of fungal cells makes the identification of novel anti-fungal agents slow and difficult. Increasing global temperature and a humid environment conducive to fungal growth may lead to a fungal endemic or a pandemic. The continuous increase in the population of immunocompromised individuals and falling immunity forced pharmaceutical companies to look for alternative strategies for better managing the global fungal burden. Prevention of infectious diseases by vaccines can be the right choice. Recent success and safe application of mRNA-based vaccines can play a crucial role in our quest to overcome anti-fungal resistance. Expressing fungal cell surface proteins in human subjects using mRNA technology may be sufficient to raise immune response to protect against future fungal infection. The success of mRNA-based anti-fungal vaccines will heavily depend on the identification of fungal surface proteins which are highly immunogenic and have no or least side effects in human subjects. The present review discusses why it is essential to look for anti-fungal vaccines and how vaccines, in general, and mRNA-based vaccines, in particular, can be the right choice in tackling the problem of rising anti-fungal resistance.

Fungal Vaccine Development: State of the Art and Perspectives Using Immunoinformatics

Fungal infections represent a serious global health problem, causing damage to health and the economy on the scale of millions. Although vaccines are the most effective therapeutic approach used to combat infectious agents, at the moment, no fungal vaccine has been approved for use in humans. However, the scientific community has been working hard to overcome this challenge. In this sense, we aim to describe here an update on the development of fungal vaccines and the progress of methodological and experimental immunotherapies against fungal infections. In addition, advances in immunoinformatic tools are described as an important aid by which to overcome the difficulty of achieving success in fungal vaccine development. In silico approaches are great options for the most important and difficult questions regarding the attainment of an efficient fungal vaccine. Here, we suggest how bioinformatic tools could contribute, considering the main challenges, to an effective fungal vaccine.

Identification of protein biomarkers of attenuation and immunogenicity of centrin or p27 gene deleted live vaccine candidates of Leishmania against visceral leishmaniasis

Currently, no licensed vaccine is available for human visceral leishmaniasis (VL), a fatal disease caused by the protozoan parasite Leishmania donovani. Two of our live attenuated L. donovani vaccine candidates, either deleted for Centrin1 (LdCen1^-/-) or p27 gene (Ldp27^-/-), that display reduced growth in macrophages were studied to be safe, immunogenic and protective against VL in various animal models. This report involves the identification of differentially expressed proteins, their related pathways and its underlying mechanism in the intracellular stage of these parasites, using Isobaric Tags for Relative and Absolute Quantitation (iTRAQ) methods. Out of 50-60 proteins, found to be differentially expressed in these mutant parasites, 36 were found to be common in both the parasites. Such proteins mainly belong to the functional categories viz. metabolic enzymes, chaperones and stress proteins, proteins involved in translation, processing and transport and proteins involved in nucleic acid processing. Proteins known to be host protective, like Glyceraldehyde-3-phosphate dehydrogenase (GAPDH), cytochrome c, calreticulin and those responsible for inducing immune response, namely tubulins, DEAD box RNA helicases, HSP70 and tryparedoxin, have been detected to be modulated in these parasites. Such proteins could be predicted as biomarkers, with further scope of study for their role in growth attenuation. SIGNIFICANCE: This study aims at predicting proteomic biomarkers of Leishmania parasite growth attenuation, that have immunomodulatory role in the disease leishmaniasis. Advanced studies could be helpful in establishing the role of these identified proteins in parasitic virulence and to predict the host interaction at molecular level. Also, these proteins could be exploited as attenuation markers during the development of genetically modified live attenuated parasites as vaccine candidates. These could be cross validated in varied species of Leishmania and other tyrpanosomatids for similar response towards identifying them as universal biomarkers of attenuation.

Consensus Enolase of Trypanosoma Cruzi: Evaluation of Their Immunogenic Properties Using a Bioinformatics Approach

There is currently no vaccine against American trypanosomiasis, caused by the parasite Trypanosoma cruzi. This is due to the genomic variation observed in the six DTUs of T. cruzi. This work aims to propose a consensus sequence of the enolase protein from different strains of T. cruzi and mainly evaluate its immunogenic properties at the bioinformatic level. From specialized databases, 15 sequences of the enolase gene were aligned to obtain a consensus sequence, where this sequence was modeled and then evaluated and validated through different bioinformatic programs to learn their immunogenic potential. Finally, chimeric peptides were designed with the most representative epitopes. The results showed high immunogenic potential with six epitopes for MHC-I, and seven epitopes for MHC-II, all of which were highly representative of the enolase present in strains from the American continent as well as five epitopes for B cells. Regarding the computational modeling, molecular docking with Toll-like receptors showed a high affinity and low constant of dissociation, which could lead to an innate-type immune response that helps to eliminate the parasite. In conclusion, the consensus sequence proposed for enolase is capable of providing an ideal immune response; however, the experimental evaluation of this enolase consensus and their chimeric peptides should be a high priority to develop a vaccine against Chagas disease.

Cytoskeletal Alteration Is an Early Cellular Response in Pulmonary Epithelium Infected with Aspergillus fumigatus Rather than Scedosporium apiospermum

Invasive aspergillosis and scedosporiosis are life-threatening fungal infections with similar clinical manifestations in immunocompromised patients. Contrarily, Scedosporium apiospermum is susceptible to some azole derivative but often resistant to amphotericin B. Histopathological examination alone cannot diagnose these two fungal species. Pathogenesis studies could contribute to explore candidate protein markers for new diagnosis and treatment methods leading to a decrease in mortality. In the present study, proteomics was conducted to identify significantly altered proteins in A549 cells infected with or without Aspergillus fumigatus and S. apiospermum as measured at initial invasion. Protein validation was performed with immunogold labelling alongside immunohistochemical techniques in infected A549 cells and lungs from murine models. Further, cytokine production was measured, using the Bio-Plex-Multiplex immunoassay. The cytoskeletal proteins HSPA9, PA2G4, VAT1, PSMA2, PEX1, PTGES3, KRT1, KRT9, CLIP1 and CLEC20A were mainly changed during A. fumigatus infection, while the immunologically activated proteins WNT7A, GAPDH and ANXA2 were principally altered during S. apiospermum infection. These proteins are involved in fungal internalisation and structural destruction leading to pulmonary disorders. Interleukin (IL)-21, IL-1α, IL-22, IL-2, IL-8, IL-12, IL-17A, interferon-γ and tumour necrosis factor-α were upregulated in both aspergillosis and scedosporiosis, although more predominately in the latter, in accordance with chitin synthase-1 and matrix metalloproteinase levels. Our results demonstrated that during invasion, A. fumigatus primarily altered host cellular integrity, whereas S. apiospermum chiefly induced and extensively modulated host immune responses.

Hypha essential genes in Candida albicans pathogenesis of oral lichen planus: an in-vitro study

BACKGROUND

Hypha essential genes (HEGs) of Candida Albicans have been emerging into scholar's attention, little known about their functions in oral lichen planus (OLP) with an uncovered etiology. This research aimed to observe necessary genes in biphasic C. albicans from OLP and study their relevance in pathogenesis, so as to evaluate possible roles of morphologic switching in etiology of OLP.

METHODS

Samples were collected from OLP lesions of patients, mycelia were cultured and total RNA was extracted then subjected to reverse transcription-PCR and real-time PCR.

RESULTS

HWP1 and HGC1 were significantly expressed in hyphae phase and weakly detected in yeast phase, while there was no significant difference of EFG1, ALS3, and ECE1 between in yeast and mycelia.

CONCLUSION

HGC1 and HWP1 were confirmed to be hypha essential genes, with HGC1 for hypha morphogenesis and HWP1 for adhesion invasion in pathogenesis of C. albicans in OLP. ALS3, ECE1 and EFG1 played minor roles in hyphae maintenance and adhesion for hyphae. These might be deemed as hints for the etiology of OLP and indicate HGC1 and HWP1 to be a priority of potential drug target.

The Role of B-Cells and Antibodies against Candida Vaccine Antigens in Invasive Candidiasis

Systemic candidiasis is an invasive fungal infection caused by members of the genus Candida. The recent emergence of antifungal drug resistance and increased incidences of infections caused by non-albicans Candida species merit the need for developing immune therapies against Candida infections. Although the role of cellular immune responses in anti-Candida immunity is well established, less is known about the role of humoral immunity against systemic candidiasis. This review summarizes currently available information on humoral immune responses induced by several promising Candida vaccine candidates, which have been identified in the past few decades. The protective antibody and B-cell responses generated by polysaccharide antigens such as mannan, β-glucan, and laminarin, as well as protein antigens like agglutinin-like sequence gene (Als3), secreted aspartyl proteinase (Sap2), heat shock protein (Hsp90), hyphally-regulated protein (Hyr1), hyphal wall protein (Hwp1), enolase (Eno), phospholipase (PLB), pyruvate kinase (Pk), fructose bisphosphate aldolase (Fba1), superoxide dismutase gene (Sod5) and malate dehydrogenase (Mdh1), are outlined. As per studies reviewed, antibodies induced in response to leading Candida vaccine candidates contribute to protection against systemic candidiasis by utilizing a variety of mechanisms such as opsonization, complement fixation, neutralization, biofilm inhibition, direct candidacidal activity, etc. The contributions of B-cells in controlling fungal infections are also discussed. Promising results using anti-Candida monoclonal antibodies for passive antibody therapy reinforces the need for developing antibody-based therapeutics including anti-idiotypic antibodies, single-chain variable fragments, peptide mimotopes, and antibody-derived peptides. Future research involving combinatorial immunotherapies using humanized monoclonal antibodies along with antifungal drugs/cytokines may prove beneficial for treating invasive fungal infections.

Mass Spectrometry-Based Proteomic and Immunoproteomic Analyses of the Candida albicans Hyphal Secretome Reveal Diagnostic Biomarker Candidates for Invasive Candidiasis

Invasive candidiasis (IC) is associated with high morbidity and mortality in hospitalized patients if not diagnosed early. Long-term use of central venous catheters is a predisposing factor for IC. Hyphal forms of Candida albicans (the major etiological agent of IC) are related to invasion of host tissues. The secreted proteins of hyphae are involved in virulence, host interaction, immune response, and immune evasion. To identify IC diagnostic biomarker candidates, we characterized the C. albicans hyphal secretome by gel-free proteomic analysis, and further assessed the antibody-reactivity patterns to this subproteome in serum pools from 12 patients with non-catheter-associated IC (ncIC), 11 patients with catheter-associated IC (cIC), and 11 non-IC patients. We identified 301 secreted hyphal proteins stratified to stem from the extracellular region, cell wall, cell surface, or intracellular compartments. ncIC and cIC patients had higher antibody levels to the hyphal secretome than non-IC patients. Seven secreted hyphal proteins were identified to be immunogenic (Bgl2, Eno1, Pgk1, Glx3, Sap5, Pra1 and Tdh3). Antibody-reactivity patterns to Bgl2, Eno1, Pgk1 and Glx3 discriminated IC patients from non-IC patients, while those to Sap5, Pra1 and Tdh3 differentiated between cIC and non-IC patients. These proteins may be useful for development of future IC diagnostic tests.

Cloning and Characterization of Immunological Properties of Haemophilus influenzae Enolase

Haemophilus influenzae is a common organism of the human upper respiratory tract; this bacterium is responsible of a wide spectrum for respiratory infections and can generate invasive diseases such as meningitis and septicemia. These infections are associated with H. influenzae encapsulated serotype b. However, the incidence of invasive disease caused by nontypeable H. influenzae (NTHi) has increased in the post-H. influenzae serotype b (Hib) vaccine era. Currently, an effective vaccine against NTHi is not available; due to this, it is important to find an antigen capable to confer protection against NTHi infection. In this study, 10 linear B cell epitopes and 13 CTL epitopes and a putative plasminogen-binding motif (₂₅₂FYNKENGMY₂₆₀) and the presence of enolase on the surface of different strains of H. influenzae were identified in the enolase sequence of H. influenzae. Both in silico and experimental results showed that recombinant enolase from H. influenzae is immunogenic that could induce a humoral immune response; this was observed mediating the generation of specific polyclonal antibodies anti-rNTHiENO that recognize typeable and nontypeable H. influenzae strains. The immunogenic properties and the superficial localization of enolase in H. influenzae, important characteristics to be considered as a new candidate for the development of a vaccine, were demonstrated.

The paradoxical and still obscure properties of fungal extracellular vesicles

Early compositional studies of fungal EVs revealed a complex combination of biomolecules, including proteins, lipids, glycans, polysaccharides, nucleic acid and pigments, indicating that these compartments could be involved with multiple functions. Curiously, some of the activities attributed to fungal EVs were already attested experimentally and are implicated with contrasting effects in vitro and in vivo. For instance, the presence of virulence factors is correlated with increased pathogenic potential. Indeed, the administration to hosts of EVs along with some fungal pathogens seems to help the disease development. However, it has been clearly shown that immunization of insects and mice with fungal EVs can protect these animals against a subsequent infection. Fungal EVs not only influence the host response, as concluded from the observation that these compartments also work as messengers between fungal organisms. In this context, despite their size characterization, other physical properties of EVs are poorly known. For instance, their stability and half-life under physiological conditions can be a crucial parameter determining their long-distance effects. In this review, we will discuss the paradoxical and still unexploited functions and properties of fungal EVs that could be determinant for their biological functions.

Targeting Unconventional Pathways in Pursuit of Novel Antifungals

The impact of invasive fungal infections on human health is a serious, but largely overlooked, public health issue. Commonly affecting the immunocompromised community, fungal infections are predominantly caused by species of Candida, Cryptococcus, and Aspergillus. Treatments are reliant on the aggressive use of pre-existing antifungal drug classes that target the fungal cell wall and membrane. Despite their frequent use, these drugs are subject to unfavorable drug-drug interactions, can cause undesirable side-effects and have compromised efficacy due to the emergence of antifungal resistance. Hence, there is a clear need to develop novel classes of antifungal drugs. A promising approach involves exploiting the metabolic needs of fungi by targeted interruption of essential metabolic pathways. This review highlights potential antifungal targets including enolase, a component of the enolase-plasminogen complex, and enzymes from the mannitol biosynthesis and purine nucleotide biosynthesis pathways. There has been increased interest in the enzymes that comprise these particular pathways and further investigation into their merits as antifungal targets and roles in fungal survival and virulence are warranted. Disruption of these vital processes by targeting unconventional pathways with small molecules or antibodies may serve as a promising approach to discovering novel classes of antifungals.

Identification of Mucor circinelloides antigens recognized by sera from immunocompromised infected mice

BACKGROUND

Mucor circinelloides is an opportunistic fungus capable of causing mucormycosis, a highly aggressive infection of quick spreading. Besides, it also has a high mortality rate due to late diagnosis and difficult treatment.

AIMS

In this study we have identified the most immunoreactive proteins of the secretome and the total protein extract of M. circinelloides using sera from immunocompromised infected mice.

METHODS

The proteins of the secretome and the total extract were analyzed by two-dimensional electrophoresis and the most immunoreactive antigens were detected by Western Blot, facing the sera of immunocompromised infected mice to the proteins obtained in both extracts of M. circinelloides.

RESULTS

Seven antigens were detected in the secretome extract, and two in the total extract, all of them corresponding only to three proteins. The enzyme enolase was detected in both extracts, while triosephosphate isomerase was detected in the secretome, and heat shock protein HSS1 in the total extract.

CONCLUSIONS

In this work the most immunoreactive antigens of the secretome and the total extract of M. circinelloides were identified. The identified proteins are well known fungal antigens and, therefore, these findings can be useful for future research into alternatives for the diagnosis and treatment of mucormycosis.

Preventing Candida albicans from subverting host plasminogen for invasive infection treatment

Candida albicans is a common fungal pathogen in humans that colonizes the skin and mucosal surfaces of the majority healthy individuals. How C. albicans disseminates into the bloodstream and causes life-threatening systemic infections in immunocompromised patients remains unclear. Plasminogen system activation can degrade a variety of structural proteins in vivo and is involved in several homeostatic processes. Here, for the first time, we characterized that C. albicans could capture and “subvert” host plasminogen to invade host epithelial cell surface barriers through cell-wall localized Eno1 protein. We found that the “subverted” plasminogen system plays an important role in development of invasive infection caused by C. albicans in mice. Base on this finding, we discovered a mouse monoclonal antibody (mAb) 12D9 targeting C. albicans Eno1, with high affinity to the ₂₅₄FYKDGKYDL₂₆₂ motif in α-helices 6, β-sheet 6 (H6S6) loop and direct blocking activity for C. albicans capture host plasminogen. mAb 12D9 could prevent C. albicans from invading human epithelial and endothelial cells, and displayed antifungal activity and synergistic effect with anidulafungin or fluconazole in proof-of-concept in vivo studies, suggesting that blocking the function of cell surface Eno1 was effective for controlling invasive infection caused by Candida spp. In summary, our study provides the evidence of C. albicans invading host by “subverting” plasminogen system, suggesting a potential novel treatment strategy for invasive fungal infections.

Vaccination with Secreted Aspartyl Proteinase 2 Protein from Candida parapsilosis Can Enhance Survival of Mice during C. tropicalis-Mediated Systemic Candidiasis

The rising incidence of non-albicans Candida species globally, along with the emergence of drug resistance, is a cause for concern. This study investigated the protective efficacy of secreted aspartyl proteinase 2 (Sap2) in systemic C. tropicalis infection. Vaccination with recombinant Sap2 (rSap2) protein from C. parapsilosis enhanced survival of mice compared to rSap2 vaccinations from C. albicans (P = 0.02), C. tropicalis (P = 0.06), and sham immunization (P = 0.04). Compared to sham-immunized mice, the fungal CFU number was significantly reduced in organs of Sap2-parapsilosis-immunized mice. Histopathologically, increased neutrophilic recruitment was observed in Sap2-parapsilosis- and Sap2-tropicalis-immunized mice. Among different rSap2 proteins, Sap2-parapsilosis vaccination induced increased titers of Sap2-specific Ig, IgG, and IgM antibodies, which could bind whole fungus. Between different groups, sera from Sap2-parapsilosis-vaccinated mice exhibited increased C. tropicalis biofilm inhibition ability in vitro and enhanced neutrophil-mediated fungal killing. Passive transfer of anti-Sap2-parapsilosis immune serum in naive mice significantly reduced fungal burdens compared to those in mice receiving anti-sham immune serum. Higher numbers of plasma cells and Candida-binding B cells in Sap2-vaccinated mice suggest a role of B cells during early stages of Sap2-mediated immune response. Additionally, increased levels of Th1/Th2/Th17 cytokines observed in Sap2-parapsilosis-vaccinated mice indicate immunomodulatory properties of Sap2. Epitope analysis performed using identified B-cell epitopes provides a basis to understand differences in immunogenicity observed among Sap2-antigens and can aid the development of a multivalent or multiepitope anti-Candida vaccine(s). In summary, our results suggest that Sap2-parapsilosis vaccination can improve mouse survival during C. tropicalis infection by inducing both humoral and cellular immunity, and higher titers of Sap2-induced antibodies are beneficial during systemic candidiasis.

Protective effect of fungal extracellular vesicles against murine candidiasis

Extracellular vesicles (EVs) are lipid bilayered compartments released by virtually all living cells, including fungi. Among the diverse molecules carried by fungal EVs, a number of immunogens, virulence factors and regulators have been characterised. Within EVs, these components could potentially impact disease outcomes by interacting with the host. From this perspective, we previously demonstrated that EVs from Candida albicans could be taken up by and activate macrophages and dendritic cells to produce cytokines and express costimulatory molecules. Moreover, pre-treatment of Galleria mellonella larvae with fungal EVs protected the insects against a subsequent lethal infection with C. albicans yeasts. These data indicate that C. albicans EVs are multi-antigenic compartments that activate the innate immune system and could be exploited as vaccine formulations. Here, we investigated whether immunisation with C. albicans EVs induces a protective effect against murine candidiasis in immunosuppressed mice. Total and fungal antigen-specific serum IgG antibodies increased by 21 days after immunisation, confirming the efficacy of the protocol. Vaccination decreased fungal burden in the liver, spleen and kidney of mice challenged with C. albicans. Splenic levels of cytokines indicated a lower inflammatory response in mice immunised with EVs when compared with EVs + Freund's adjuvant (ADJ). Higher levels of IL-12p70, TNFα and IFNγ were detected in mice vaccinated with EVs + ADJ, while IL-12p70, TGFβ, IL-4 and IL-10 were increased when no adjuvants were added. Full protection of lethally challenged mice was observed when EVs were administered, regardless the presence of adjuvant. Physical properties of the EVs were also investigated and EVs produced by C. albicans were relatively stable after storage at 4, -20 or -80°C, keeping their ability to activate dendritic cells and to protect G. mellonella against a lethal candidiasis. Our data suggest that fungal EVs could be a safe source of antigens to be exploited in vaccine formulations.

Dectin-1 Facilitates IL-18 Production for the Generation of Protective Antibodies Against Candida albicans

Invasive candidiasis (IC) is one of the leading causes of death among immunocompromised patients. Because of limited effective therapy treatment options, prevention of IC through vaccine is an appealing strategy. However, how to induce the generation of direct candidacidal antibodies in host remains unclear. Gpi7 mutant C. albicans is an avirulent strain that exposes cell wall β-(1,3)-glucans. Here, we found that vaccination with the gpi7 mutant strain could protect mice against invasive candidiasis caused by C. albicans and non-albicans Candida spp. The protective effects induced by gpi7 mutant relied on long-lived plasma cells (LLPCs) secreting protective antibodies against C. albicans. Clinically, we verified a similar profile of IgG antibodies in the serum samples from patients recovering from IC to those from gpi7 mutant-vaccinated mice. Mechanistically, we found cell wall β-(1,3)-glucan of gpi7 mutant facilitated Dectin-1 receptor dependent nuclear translocation of non-canonical NF-κB subunit RelB in macrophages and subsequent IL-18 secretion, which primed protective antibodies generation in vivo. Together, our study demonstrate that Dectin-1 engagement could trigger RelB activation to prime IL-18 expression and established a new paradigm for consideration of the link between Dectin-1 mediated innate immune response and adaptive humoral immunity, suggesting a previously unknown active vaccination strategy against Candida spp. infection.

A safe non-toxic Brucella abortus ghosts induce immune responses and confer protection in BALB/c mice

Brucellosis, which is caused by Brucella spp., is an important zoonotic infectious disease that can cause great hazard to public health and safety. However, the current vaccines have several drawbacks, including residual virulence for animals and humans. Bacterial ghost is the empty envelopes of bacteria, which emerge as a proper vaccine candidate. With the purpose of generating B. abortus ghosts and investigating the immunogenicity of bacterial ghosts as vaccine candidate, we used homologous recombination and bacterial ghost technologies to construct 2308ΔgntR ghost strain. Mice were injected with 2308ΔgntR ghost and the safety and immunogenicity of ghost were further evaluated. The mice inoculated with ghost showed no splenomegaly. The 2308ΔgntR ghost induced high protective immunity in BALB/c mice against challenge with S2308, and elicited an anti-Brucella-specific immunoglobulin G (IgG) response and induced the secretion of interferon gamma (IFN-γ) and interleukin-4 (IL-4). Additionally, 2308ΔgntR ghost demonstrated strong spleen CD4⁺ and CD8⁺ T cell responses. These results suggest that 2308ΔgntR ghost is a potential vaccine candidate and may represent a promising new approach for vaccination against Brucella infection.

The monoclonal antibody Ca37, developed against Candida albicans alcohol dehydrogenase, inhibits the yeast in vitro and in vivo

Candida albicans is a commensal yeast able to cause life threatening invasive infections particularly in immunocompromised patients. Despite the availability of antifungal treatments, mortality rates are still unacceptably high and drug resistance is increasing. We, therefore, generated the Ca37 monoclonal antibody against the C. albicans alcohol dehydrogenase (Adh) 1. Our data showed that Ca37 was able to detect C. albicans cells, and it bound to Adh1 in yeast and Adh2 in hyphae among the cell wall-associated proteins. Moreover, Ca37 was able to inhibit candidal growth following 18 h incubation time and reduced the minimal inhibitory concentration of amphotericin B or fluconazole when used in combination with those antifungals. In addition, the antibody prolonged the survival of C. albicans infected-Galleria mellonella larvae, when C. albicans was exposed to antibody prior to inoculating G. mellonella or by direct application as a therapeutic agent on infected larvae. In conclusion, the Ca37 monoclonal antibody proved to be effective against C. albicans, both in vitro and in vivo, and to act together with antifungal drugs, suggesting Adh proteins could be interesting therapeutic targets against this pathogen.

α-Enolase as a novel vaccine candidate against Streptococcus dysgalactiae infection in cobia (Rachycentron canadum L.)

Streptococcus dysgalactiae is an important pathogenic bacterium that has caused economic loss for the cobia industry in Taiwan, ROC. This study presents a highly effective subunit vaccine composed of a moonlight protein, α-enolase, for the prevention of S. dysgalactiae infection. First, α-enolase was cloned, transformed, and expressed in E. coli for production of recombinant protein. Then, the protective efficacies of α-enolase recombinant protein were evaluated in combination with either a pro-inflammatory cytokine, TNF-α, or an oil adjuvant, ISA 763 AVG. The results showed that the combination of α-enolase and ISA 763 AVG was highly protective (RPS = 88.89%), while a negative effect was found in the group immunised with α-enolase adjuvanted with TNF-α (RPS = 22.22%). A further study was conducted with double dose of ISA 763 AVG, which led to an increased RPS value of 97.37%. Moreover, immunised cobia exhibited significantly greater lysozyme activity, antibody responses, and expression of certain immune-related genes post-challenge. Altogether, our results demonstrated that a combination of α-enolase recombinant protein with ISA 763 AVG adjuvant is a promising vaccine that can be employed for protection of cobia against S. dysgalactiae infection.

Immunization with recombinant enolase of Sporothrix spp. (rSsEno) confers effective protection against sporotrichosis in mice

In recent years, research has focused on the immunoreactive components of the Sporothrix schenckii cell wall that can be relevant targets for preventive and therapeutic vaccines against sporotrichosis, an emergent worldwide mycosis. In a previous study, we identified a 47-kDa enolase as an immunodominant antigen in mice vaccinated with an adjuvanted mixture of S. schenckii cell wall proteins. Here, we sought to assess the protective potential of a Sporothrix spp. recombinant enolase (rSsEno) formulated with or without the adjuvant Montanide Pet-GelA (PGA) against the S. brasiliensis infection in mice. Mice that were immunized with rSsEno plus PGA showed increased antibody titters against rSsEno and increased median survival time when challenged with S. brasiliensis as compared with mice that had not been immunized or that were immunized with rSsEno alone. Immunization with rSsEno plus PGA induced a predominantly T-helper 1 cytokine pattern after in vitro stimulation of splenic cells with rSsEno: elevated levels of IFN-γ and IL-2, as well as of other cytokines involved in host defense against sporotrichosis, such as TNF-alpha, IL-6, and IL-4. Furthermore, we show for the first time the presence of enolase in the cell wall of both S. schenckii and S. brasiliensis. As a whole, our results suggest that enolase could be used as a potential antigenic target for vaccinal purposes against sporotrichosis.

Alcohol dehydrogenase of Candida albicans triggers differentiation of THP-1 cells into macrophages

Candida albicans proteins located on the cell wall and in the cytoplasm have gained great attention because they are not only involved in cellular metabolism and the maintenance of integrity but also interact with host immune systems. Previous research has reported that enolase from C. albicans exhibits high immunogenicity and effectively protects mice against disseminated candidiasis. In this study, alcohol dehydrogenase (ADH) of C. albicans was cloned and purified for the first time, and this study focused on evaluating its effects on the differentiation of the human monocytic cell line THP-1. The morphological features of THP-1 cells exposed to ADH were similar to those of phorbol-12-myristate acetate-differentiated (PMA-differentiated) macrophages. Functionally, ADH enhanced the adhesion, phagocytosis, and killing capacities of THP-1 cells. A flow cytometric assay demonstrated that ADH-induced THP-1 cells significantly increased CD86 and CD11b expression. The production of IL-1β, IL-6, and TNF-α by cells increased in the presence of ADH. As expected, after pretreatment with a MEK inhibitor (U0126), ADH-induced THP-1 cells exhibited unaltered morphological features, eliminated ERK1/2 phosphorylation, prevented CD86/CD11b upregulation and inhibited pro-inflammatory cytokine increase. Collectively, these results suggest that ADH enables THP-1 cells to differentiate into macrophages via the ERK pathway, and it may play an important role in the immune response against fungal invasion.

Fungal vaccines, mechanism of actions and immunology: A comprehensive review

Fungal infections include a wide range of opportunistic and invasive diseases. Two of four major fatal diseases in patients with human immunodeficiency virus (HIV) infection are related to the fungal infections, cryptococcosis, and pneumocystosis. Disseminated candidiasis and different clinical forms of aspergillosis annually impose expensive medical costs to governments and hospitalized patients and ultimately lead to high mortality rates. Therefore, urgent implementations are necessary to prevent the expansion of these diseases. Designing an effective vaccine is one of the most important approaches in this field. So far, numerous efforts have been carried out in developing an effective vaccine against fungal infections. Some of these challenges engaged in different stages of clinical trials but none of them could be approved by the United States Food and Drug Administration (FDA). Here, in addition to have a comprehensive overview on the data from studied vaccine programs, we will discuss the immunology response against fungal infections. Moreover, it will be attempted to clarify the underlying immune mechanisms of vaccines targeting different fungal infections that are crucial for designing an effective vaccination strategy.

Development and evaluation of in murine model, of an improved live-vaccine candidate against brucellosis from to Brucella melitensis vjbR deletion mutant

Brucellosis is an infectious disease that brings enormous economic burdens for developing countries. The Brucella melitensis (B. melitensis) M5-90 vaccine strain (M5-90) has been used on a large scale in China, but may cause abortions if given to pregnant goats or sheep subcutaneously during the late stages of gestation. Moreover, the vaccine M5-90 cannot differentiate natural from vaccinated infection. Therefore, a safer and more potent M5-90 vaccine is required. In this study, a vjbR mutant of M5-90 (M5-90ΔvjbR) was constructed and overcame these drawbacks. M5-90ΔvjbR strain showed reduced survival capability in murine macrophages (RAW 264.7) and BALB/c mice and induced high protective immunity in mice. In addition, M5-90ΔvjbR induced an anti-Brucella-specific immunoglobulin G (IgG) response and stimulated the expression of gamma interferon (INF-γ) and interleukin-4 (IL-4) in vaccinated mice. Furthermore, M5-90ΔvjbR induced IgG response and stimulated the secretion of IFN-γ and IL-4 in immunized sheep. Moreover, the VjbR antigen allowed serological differentiation between infected and vaccinated animals. These results suggest that M5-90ΔvjbR is an ideal live attenuated and efficacious live vaccine candidate against B. melitensis 16 M infection.

Recombinant Enolase of Trypanosoma cruzi as a Novel Vaccine Candidate against Chagas Disease in a Mouse Model of Acute Infection

Trypanosoma cruzi is the protozoan parasite that causes Chagas disease, which is considered by the World Health Organization to be a neglected tropical disease. Two drugs exist for the treatment of Chagas disease, nifurtimox and benznidazole; they are only effective in the acute phase, and a vaccine is currently not available. In this study, we used the recombinant enolase from T. cruzi H8 strain (MHOM/MX/1992/H8 Yucatán) (rTcENO) and its encoding DNA (pBKTcENO) to immunize mice and evaluate their protective effects in an experimental murine model of acute phase infection. Our results showed that mice vaccinated with rTcENO or its encoding DNA were able to generate typical specific antibodies (IgG1, IgG2a, and IgG2b), suggesting that a mixed Th1/Th2 immune response was induced. The parasite burden in the blood was reduced to 69.8% and 71% in mice vaccinated with rTcENO and pBKTcENO, respectively. The group vaccinated with rTcENO achieved 75% survival, in contrast to the group vaccinated with pBKTcENO that showed no survival in comparison to the control groups. Moreover, rTcENO immunization elevated the production of IFN-γ and IL-2 after the parasite challenge, suggesting that the Th1-type immune response was polarized. These results indicated that rTcENO could be used as a vaccine against Chagas disease.

Brucella abortus phosphoglyceromutase and dihydrodipicolinate reductase induce Th1 and Th2-related immune responses

Brucellae are intracellular bacterial pathogens that cause Brucellosis, bringing great economic burdens to developing countries. The pathogenic mechanisms of Brucella are still poorly understood. Earlier immune response plays an important role in the Brucella infection. Phosphoglyceromutase (PGM) and dihydrodipicolinate reductase (DapB) were cloned, expressed, purified, and their immunocompetence was analyzed. Cytokines were detected by murine macrophages (RAW 264.7) and splenocytes that stimulated with the two recombinant proteins. The immune responses were analyzed by ELISA from mice with the two recombinant proteins immunized. TNF-α, IL-6 and IL-8 were produced in stimulated RAW 264.7 cells and splenocytes. Th1-type cytokines, IFN-γ and IL-2, induced in RAW 264.7 cells and splenocytes were higher then Th2-type cytokines, IL-4 and IL-5. Th2-related immune response was induced in splenocytes obtained 35 days after mice immunized with the two proteins. The production of IgG1 was higher than IgG2a in immunized mice. Taken together, our results demonstrated that the two proteins could induce Th1 and Th2-type immune responses in vivo and in vitro.

Outer Membrane Protein 25 of Brucella Activates Mitogen-Activated Protein Kinase Signal Pathway in Human Trophoblast Cells

Outer membrane protein 25 (OMP25), a virulence factor from Brucella, plays an important role in maintaining the structural stability of Brucella. Mitogen-activated protein kinase (MAPK) signal pathway widely exists in eukaryotic cells. In this study, human trophoblast cell line HPT-8 and BALB/c mice were infected with Brucella abortus 2308 strain (S2308) and 2308ΔOmp25 mutant strain. The expression of cytokines and activation of MAPK signal pathway were detected. We found that the expressions of tumor necrosis factor-α, interleukin-1, and interleukin-10 (IL-10) were increased in HPT-8 cells infected with S2308 and 2308ΔOmp25 mutant. S2308 also activated p38 phosphorylation protein, extracellular-regulated protein kinases (ERK), and Jun-N-terminal kinase (JNK) from MAPK signal pathway. 2308ΔOmp25 could not activate p38, ERK, and JNK branches. Immunohistochemistry experiments showed that S2308 was able to activate phosphorylation of p38 and ERK in BABL/c mice. However, 2308ΔOmp25 could weakly activate phosphorylation of p38 and ERK. These results suggest that Omp25 played an important role in the process of Brucella activation of the MAPK signal pathway.

Deletion of the transcriptional regulator GntR down regulated the expression of Genes Related to Virulence and Conferred Protection against Wild-Type Brucella Challenge in BALB/c Mice

Brucellosis, which is caused by Brucella spp., is a zoonotic infectious disease that can cause great hazard to public health and safety. The virulence of Brucella is essential for survive and multiply in host macrophages. GntR is a transcriptional regulator in Brucella that is required for virulence in macrophages and mice, and involved in resistance to stress responses. To determine the expression levels of target genes of GntR, we detected the expression levels of the GntR target genes in Brucella infected BALB/c mice. The results showed that several genes related to virulence, including omp25, virB1, vjbR, dnaK, htrA and hfq, were regulated by GntR during infection in BALB/c mice. Moreover, the 2308ΔgntR mutant induced high protective immunity in BALB/c mice challenge with B. abortus 2308 (S2308), and elicited an anti-Brucella-specific immunoglobulin G (IgG) response and induced the secretion of gamma interferon (IFN-γ) and interleukin-4 (IL-4). All together, these results indicated that gntR promoted the virulence of Brucella. The 2308ΔgntR was significantly attenuated in macrophages and mice and induced protective immune response during infection, suggested that 2308ΔgntR mutant is an attractive candidate for the design of a live attenuated vaccine against Brucella.

Aspartic Proteases and Major Cell Wall Components in Candida albicans Trigger the Release of Neutrophil Extracellular Traps

Neutrophils use different mechanisms to cope with pathogens that invade the host organism. The most intriguing of these responses is a release of neutrophil extracellular traps (NETs) composed of decondensed chromatin and granular proteins with antimicrobial activity. An important potential target of NETs is Candida albicans-an opportunistic fungal pathogen that employs morphological and phenotype switches and biofilm formation during contact with neutrophils, accompanied by changes in epitope exposition that mask the pathogen from host recognition. These processes differ depending on infection conditions and are thus influenced by the surrounding environment. In the current study, we compared the NET release by neutrophils upon contact with purified main candidal cell surface components. We show here for the first time that in addition to the main cell wall-building polysaccharides (mannans and β-glucans), secreted aspartic proteases (Saps) trigger NETs with variable intensities. The most efficient NET-releasing response is with Sap4 and Sap6, which are known to be secreted by fungal hyphae. This involves mixed, ROS-dependent and ROS-independent signaling pathways, mainly through interactions with the CD11b receptor. In comparison, upon contact with the cell wall-bound Sap9 and Sap10, neutrophils responded via a ROS-dependent mechanism using CD16 and CD18 receptors for protease recognition. In addition to the Saps tested, the actuation of selected mediating kinases (Src, Syk, PI3K, and ERK) was also investigated. β-Glucans were found to trigger a ROS-dependent process of NET production with engagement of Dectin-1 as well as CD11b and CD18 receptors. Mannans were observed to be recognized by TLRs, CD14, and Dectin-1 receptors and triggered NET release mainly via a ROS-independent pathway. Our results thus strongly suggest that neutrophils activate NET production in response to different candidal components that are presented locally at low concentrations at the initial stages of infection. However, NET release seemed to be blocked by increasing numbers of fungal cells.

Identification of proteins involved in the adhesionof Candida species to different medical devices

Adhesion is the first step for Candida species to form biofilms on medical devices implanted in the human host. Both the physicochemical nature of the biomaterial and cell wall proteins (CWP) of the pathogen play a determinant role in the process. While it is true that some CWP have been identified in vitro, little is known about the CWP of pathogenic species of Candida involved in adhesion. On this background, we considered it important to investigate the potential role of CWP of C. albicans, C. glabrata, C. krusei and C. parapsilosis in adhesion to different medical devices. Our results indicate that the four species strongly adher to polyvinyl chloride (PVC) devices, followed by polyurethane and finally by silicone. It was interesting to identify fructose-bisphosphate aldolase (Fba1) and enolase 1 (Eno1) as the CWP involved in adhesion of C. albicans, C. glabrata and C. krusei to PVC devices whereas phosphoglycerate kinase (Pgk) and Eno1 allow C. parapsilosis to adher to silicone-made implants. Results presented here suggest that these CWP participate in the initial event of adhesion and are probably followed by other proteins that covalently bind to the biomaterial thus providing conditions for biofilm formation and eventually the onset of infection.

Brucella abortus 2308ΔNodVΔNodW double-mutant is highly attenuated and confers protection against wild-type challenge in BALB/c mice

Brucellosis is an important zoonotic disease of worldwide distribution, which causes animal and human disease. However, the current Brucella abortus (B. abortus) vaccines (S19 and RB51) have several drawbacks, including residual virulence for animals and humans. Moreover, S19 cannot allow serological differentiation between infected and vaccinated animals. We constructed double deletion (ΔNodVΔNodW) mutant from virulent B. abortus 2308 (S2308) by deleting the genes encoding two-component regulatory system (TCS) in chromosome II in S2308.2308ΔNodVΔNodW was significantly reduced survival in murine macrophages (RAW 264.7) and BALB/c mice. Moreover, the inoculated mice showed no splenomegaly. The mutant induced high protective immunity in BALB/c mice against challenge with S2308, and elicited an anti-Brucella-specific immunoglobulin G (IgG) response and induced the secretion of gamma interferon (IFN-γ) and interleukin-4 (IL-4). Moreover, NODV and NODW antigens would allow the serological differentiation between infected and vaccinated animals. These results suggest that 2308ΔNodVΔNodW mutant is a potential live attenuated vaccine candidate and can be used effectively against bovine brucellosis.

Assessment of Post-Vaccination Phagocytic Activation Using Candida albicans Killing Assays

Candida albicans is an important opportunistic fungal pathogen. It is now the fourth leading cause of nosocomial bloodstream infections and a great threat to the immuncompromised patients attributed to the disseminated candidiasis with the mortality up to 40%. Phagocytic cells are the first line of defense against Candida infections. Antibodies induced by vaccination can effectively enhance the capacities of phagocytosis and killing of neutrophils and macrophages. In this chapter, flow cytometric analysis (FACS) and killing assay by plate culture methods are introduced to evaluate the phagocytosis and killing of strains of Candida albicans opsonized with immune serum obtained from mice vaccinated with yeast and recombinant enolase.

Serum Antibody Profile during Colonization of the Mouse Gut by Candida albicans: Relevance for Protection during Systemic Infection

Candida albicans is a commensal microorganism in the oral cavity and gastrointestinal and urogenital tracts of most individuals that acts as an opportunistic pathogen when the host immune response is reduced. Here, we established different immunocompetent murine models to analyze the antibody responses to the C. albicans proteome during commensalism, commensalism followed by infection, and infection (C, C+I, and I models, respectively). Serum anti-C. albicans IgG antibody levels were higher in colonized mice than in infected mice. The antibody responses during gut commensalism (up to 55 days of colonization) mainly focused on C. albicans proteins involved in stress response and metabolism and differed in both models of commensalism. Different serum IgG antibody-reactivity profiles were also found over time among the three murine models. C. albicans gut colonization protected mice from an intravenous lethal fungal challenge, emphasizing the benefits of fungal gut colonization. This work highlights the importance of fungal gut colonization for future immune prophylactic therapies.

Cyclophilin and enolase are the most prevalent conidial antigens of Lomentospora prolificans recognized by healthy human salivary IgA and cross-react with Aspergillus fumigatus

PURPOSE

The study of the immunocompetent airways immune response may provide important information to improve the therapeutic efficacy against Lomentospora (Scedosporium) prolificans. So, this study aimed to identify the most prevalent conidial antigens of this multiresistant fungus recognized by healthy human salivary immunoglobulin A, and to study their expression and cross-reactivity with other fungal species.

EXPERIMENTAL DESIGN

Twenty saliva from immunocompetent donors were used to detect and identify the immunoreactive proteins by 2D immunoblotting and LC-MS/MS. Moreover, anti-Aspergillus antibodies were purified to study their cross-reactivity.

RESULTS

Ten proteins of L. prolificans conidia showed reactivity with more than 50% of the saliva samples. Among them, cyclophilin and enolase were the most prevalent antigens recognized by 85 and 80% of the samples, respectively. These enzymes were also identified on the cell wall surface of L. prolificans and on the immunomes of Scedosporium apiospermum and Scedosporium aurantiacum. Additionally, they showed cross-reactivity with the most common pathogenic filamentous fungus Aspergillus fumigatus.

CONCLUSION AND CLINICAL RELEVANCE

These results show that the immunocompetent immune response might offer a pan-fungal recognition of conserved antigens such as enolase and cyclophilins, making them potential candidates for study as therapeutic targets.

Protective effect of antigen delivery using monoolein-based liposomes in experimental hematogenously disseminated candidiasis

We evaluated the potential of a liposomal antigen delivery system (ADS) containing Candida albicans cell wall surface proteins (CWSP) in mediating protection against systemic candidiasis. Treatment of bone-marrow-derived dendritic cells with CWSP-loaded dioctadecyldimethylammonium bromide:monoolein (DODAB:MO) liposomes enhanced and prolonged their activation comparatively to free antigen, indicating that liposome-entrapped CWSP were released more sustainable. Therefore, we immunized mice with CWSP either in a free form or loaded into two different DODAB:MO liposome formulations, respectively designated as ADS1 and ADS2, prior to intravenous C. albicans infection. Immunization with ADS1, but not with ADS2, conferred significant protection to infected mice, comparatively to immunization with CWSP or empty liposomes as control. ADS1-immunized mice presented significantly higher serum levels of C. albicans-specific antibodies that enhanced phagocytosis of this fungus. In these mice, a mixed cytokine production profile was observed encompassing IFN-γ, IL-4, IL-17A and IL-10. Nevertheless, only production of IL-4, IL-17 and IL-10 was higher than in controls. In this study we demonstrated that DODAB:MO liposomes enhance the immunogenicity of C. albicans antigens and host protection in a murine model of systemic candidiasis. Therefore, this liposomal adjuvant could be a promising candidate to assess in vaccination against this pathogenic fungus.

STATEMENT OF SIGNIFICANCE

This work describes the immunomodulation capacity of the previously validated antigen delivery system (ADS) composed by dioctadecyldimethylammonium bromide (DODAB) and monoolein (MO) lipids incorporating the cell wall surface proteins (CWSP) from C. albicans. Here, we not only present the ability of this system in facilitating antigen uptake by DCs in vitro, but also that this system induces higher levels of pro-inflammatory cytokines and opsonizing specific IgG antibodies in serum of mice immunized subcutaneously. We show that the ADS are efficient nanocarrier and modulate the immune response against intravenous C. albicans infection favoring mouse protection. In sum, we show that the incorporation of C. albicans antigens in DODAB:MO nanocarries are a promising vaccine strategy against C. albicans fungal infection.

Extracellular Vesicle-Associated Transitory Cell Wall Components and Their Impact on the Interaction of Fungi with Host Cells

Classic cell wall components of fungi comprise the polysaccharides glucans and chitin, in association with glycoproteins and pigments. During the last decade, however, system biology approaches clearly demonstrated that the composition of fungal cell walls include atypical molecules historically associated with intracellular or membrane locations. Elucidation of mechanisms by which many fungal molecules are exported to the extracellular space suggested that these atypical components are transitorily located to the cell wall. The presence of extracellular vesicles (EVs) at the fungal cell wall and in culture supernatants of distinct pathogenic species suggested a highly functional mechanism of molecular export in these organisms. Thus, the passage of EVs through fungal cell walls suggests remarkable molecular diversity and, consequently, a potentially variable influence on the host antifungal response. On the basis of information derived from the proteomic characterization of fungal EVs from the yeasts Cryptoccocus neoformans and Candida albicans and the dimorphic fungi Histoplasma capsulatum and Paracoccidioides brasiliensis, our manuscript is focused on the clear view that the fungal cell wall is much more complex than previously thought.

Comparative Analysis of Cellular Immune Responses in Treated Leishmania Patients and Hamsters against Recombinant Th1 Stimulatory Proteins of Leishmania donovani

Our prior studies demonstrated that cellular response of T helper 1 (Th1) type was generated by a soluble antigenic fraction (ranging from 89.9 to 97.1 kDa) of Leishmania donovani promastigote, in treated Leishmania patients as well as hamsters and showed significant prophylactic potential against experimental visceral leishmaniasis (VL). Eighteen Th1 stimulatory proteins were identified through proteomic analysis of this subfraction, out of which 15 were developed as recombinant proteins. In the present work, we have evaluated these 15 recombinant proteins simultaneously for their comparative cellular responses in treated Leishmania patients and hamsters. Six proteins viz. elongation factor-2, enolase, aldolase, triose phosphate isomerase, protein disulfide isomerase, and p45 emerged as most immunogenic as they produced a significant lymphoproliferative response, nitric oxide generation and Th1 cytokine response in PBMCs and lymphocytes of treated Leishmania patients and hamsters respectively. The results suggested that these proteins may be exploited for developing a successful poly-protein and/or poly-epitope vaccine against VL.

The Brucella melitensis M5-90 phosphoglucomutase (PGM) mutant is attenuated and confers protection against wild-type challenge in BALB/c mice

Brucellae are Gram-negative intracellular bacterial pathogens that infect humans and animals, bringing great economic burdens to developing countries. Live attenuated Brucella vaccines (strain M5-90 or others) are the most efficient means for prevention and control of animal brucellosis. However, these vaccines have several drawbacks, including residual virulence in animals, and difficulties in differentiating natural infection from vaccine immunization, which limit their application. A vaccine that can differentiate infection from immunization will have extensive applications. A Brucella melitensis (B. melitensis) strain M5-90 pgm mutant (M5-90Δpgm) was constructed to overcome these drawbacks. M5-90Δpgm showed significantly reduced survival in embryonic trophoblast cells and in mice, and induced high protective immunity in BALB/c mice. Moreover, M5-90Δpgm elicited an anti-Brucella-specific immunoglobulin G response and induced the secretion of gamma interferon (IFN-γ) and interleukin-2 (IL-2). In addition, M5-90Δpgm induced the secretion of IFN-γ in immunized sheep. Serum samples from sheep inoculated with M5-90Δpgm were negative by the Rose Bengal Plate Test (RBPT) and Standard Tube Agglutination Test (STAT). Furthermore, the PGM antigen allowed serological differentiation between infected and vaccinated animals. These results suggest that M5-90Δpgm is an ideal live attenuated vaccine candidate against B. melitensis 16 M and deserves further evaluation for vaccine development.

Production of a Chaetomium globosum enolase monoclonal antibody

Chaetomium globosum is a hydrophilic fungal species and a contaminant of water-damaged building materials in North America. Methods to detect Chaetomium species include subjective identification of ascospores, viable culture, or molecular-based detection methods. In this study, we describe the production and initial characterization of a monoclonal antibody (MAb) for C. globosum enolase. MAb 1C7, a murine IgG1 isotype MAb, was produced and reacted with recombinant C. globosum enolase (rCgEno) in an enzyme-linked immunosorbent assay and with a putative C. globosum enolase in a Western blot. Epitope mapping showed MAb 1C7 specific reactivity to an enolase decapeptide, LTYEELANLY, that is highly conserved within the fungal class Sordariomycetes. Cross-reactivity studies showed MAb 1C7 reactivity to C. atrobrunneum but not C. indicum. MAb 1C7 did not react with enolase from Aspergillus fumigatus, which is divergent in only two amino acids within this epitope. The results of this study suggest potential utility of MAb 1C7 in Western blot applications for the detection of Chaetomium and other Sordariomycetes species.

The glycolytic enzyme enolase represents a plasminogen-binding protein on the surface of a wide variety of medically important fungal species

Allergies are an increasing issue in human health and can, eventually, cause severe anaphylactic shock. Aspergillus fumigatus and Candida albicans are leading causes of life-threatening invasive fungal infections in immunocompromised patients, but can also cause severe allergic responses in otherwise healthy individuals. The glycolytic enzyme enolase is known as a major allergen despite its function in intracellular metabolism. Therefore, its presentation on surfaces of different fungal species was investigated by using antibodies raised against recombinant enolases from A. fumigatus and C. albicans. Examination of antibody specificity revealed cross-reactivity to cell-free extracts from Aspergillus terreus, Aspergillus flavus, Aspergillus nidulans and Candida glabrata, but not against any of the three human enolases. Antibody specificity was further confirmed by hybridization with other recombinant fungal enolases, where the antibodies recognized different subsets of fungal enolases. When surface presentation of enolase was tested on intact fungal cells, a positive staining was obtained with those antibodies that also recognized the enzyme from the respective cell-free extract. This implies a general surface presentation of this glycolytic enzyme among fungal species and provides hints for its predominant recognition as an allergen. Additionally, A. fumigatus and C. albicans enolase bound to human plasminogen, which remained accessible for the plasminogen activator uPA. This implies a potential role of enolase in the invasion and dissemination process during fungal infections.

Moonlight-like proteins of the cell wall protect sessile cells of Candida from oxidative stress

Biofilms of Candida species are associated with high morbidity and hospital mortality. Candida forms biofilms by adhering to human host epithelium through cell wall proteins (CWP) and simultaneously neutralizing the reactive oxygen species (ROS) produced during the respiratory burst by phagocytic cells. The purpose of this paper is to identify the CWP of Candida albicans, Candida glabrata, Candida krusei and Candida parapsilosis expressed after exposure to different concentrations of H2O2 using a proteomic approach. CWP obtained from sessile cells, both treated and untreated with the oxidizing agent, were resolved by one and two-dimensional (2D-PAGE) gels and identified by liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. Some of these proteins were identified and found to correspond to moonlighting CWP such as: (i) glycolytic enzymes, (ii) heat shock, (iii) OSR proteins, (iv) general metabolic enzymes and (v) highly conserved proteins, which are up- or down-regulated in the presence or absence of ROS. We also found that the expression of these CWP is different for each Candida species. Moreover, RT-PCR assays allowed us to demonstrate that transcription of the gene coding for Eno1, one of the moonlight-like CWP identified in response to the oxidant agent, is differentially regulated. To our knowledge this is the first demonstration that, in response to oxidative stress, each species of Candida, differentially regulates the expression of moonlighting CWP, which may protect the organism from the ROS generated during phagocytosis. Presumptively, these proteins allow the pathogen to adhere and form a biofilm, and eventually cause invasive candidiasis in the human host. We propose that, in addition to the antioxidant mechanisms present in Candida, the moonlighting CWP also confer protection to these pathogens from oxidative stress.

A cell wall protein-based vaccine candidate induce protective immune response against Sporothrix schenckii infection

Sporotrichosis is a subcutaneous mycosis caused by several closely related thermo-dimorphic fungi of the Sporothrix schenckii species complex, affecting humans and other mammals. In the last few years, new strategies have been proposed for controlling sporotrichosis owning to concerns about its growing incidence in humans, cats, and dogs in Brazil, as well as the toxicity and limited efficacy of conventional antifungal drugs. In this study, we assessed the immunogenicity and protective properties of two aluminum hydroxide (AH)-adsorbed S. schenckii cell wall protein (ssCWP)-based vaccine formulations in a mouse model of systemic S. schenckii infection. Fractioning by SDS-PAGE revealed nine protein bands, two of which were functionally characterized: a 44kDa peptide hydrolase and a 47kDa enolase, which was predicted to be an adhesin. Sera from immunized mice recognized the 47kDa enolase and another unidentified 71kDa protein, whereas serum from S. schenckii-infected mice recognized both these proteins plus another unidentified 9.4kDa protein. Furthermore, opsonization with the anti-ssCWP sera led to markedly increased phagocytosis and was able to strongly inhibit the fungus' adhesion to fibroblasts. Immunization with the higher-dose AH-adjuvanted formulation led to increased ex vivo release of IL-12, IFN-γ, IL-4, and IL-17, whereas only IL-12 and IFN-γ were induced by the higher-dose non-adjuvanted formulation. Lastly, passive transference of the higher-dose AH-adjuvanted formulation's anti-ssCWP serum was able to afford in vivo protection in a subsequent challenge with S. schenckii, becoming a viable vaccine candidate for further testing.